The over-all objective of this proposal is to determine the relative and absolute contributions of mechanical (inertia, elasticity, friction) and neural feedback (reflex) properties of an intact skeletal motor control system of man to voluntary and involuntary motion produced by the system. The contribution made by these properties to limb motion will be tested and described in terms of normal (and abnormal) values of the parameters of a lumped-parameter model. Experimental testing will involve determination of coherence, gain, and phase values between the demodulated Electromyogram (EMG) of the muscles controlling a limb and the motion (voluntary and involuntary) of that limb.